1. Field of the Invention
The present invention relates to a composite molded lens formed by press-forming and injection molding and a method for producing a composite molded lens.
2. Description Related to the Prior Art
A digital camera, a mobile terminal with a camera, or the like uses a taking lens to form an image of a subject on an image sensor. A projector uses a projector lens to project an image, which is displayed on a liquid crystal display, onto a screen. A molded lens is generally used as an optical lens such as the taking lens or the projector lens. The molded lens is produced by press-forming a preform (lens material) while the preform is heated.
The molded lens has advantages that it has high optical performance and eliminates the need for after-treatment such as grinding. However, it is difficult to form a positioning or alignment face, which is perpendicular to the optical axis, and an outer peripheral end face, which is fitted into a lens frame, of the molded lens. Hence, it is difficult to align the position of the molded lens in the lens frame or a lens barrel or to improve the accuracy of centering the molded lens. Recently, small molded lenses and large-diameter molded lenses have been developed and there has been a tendency to reduce the lens thickness relative to outer-diameter dimensions. In a case where the thickness of the molded lens, particularly, a convex lens, is further reduced, an outer peripheral portion thereof becomes extremely thin. This makes it difficult to attach the lens frame to the molded lens. As a result, the accuracy of attaching the lens frame or the like to the molded lens is further reduced.
For this reason, it is suggested to integrally form the lens frame around the outer periphery of the lens. For example, in Japanese Examined Patent Publication No. 07-98669, first and second molds are used to apply pressure to a lens material (preform) while the lens material is heated, and thereby an optical element (lens body) is produced. During the application of the pressure, an outer peripheral portion of the optical element is squeezed out of inner side portions of the first and second molds and projects into a cavity between the first and second molds. Molten resin is filled in the cavity to form an optical element frame (lens frame) by injection molding. Thereby the optical element frame is bonded to the outer peripheral portion of the optical element, and thus an optical element (composite molded lens) is formed integrally with the optical element frame.
Japanese Patent Laid-Open Publication No. 2007-22905 also discloses producing an optical element device (composite molded lens) by use of first and second molds. Glass is press-formed with the first and second molds while being heated, and thereby an optical lens (lens body) is produced. Then resin is injection-molded to form a frame (lens frame) integrally with the optical lens. Thus, the optical element device (composite molded lens) is produced. In this optical element device, a flat portion (flange portion) is formed around the outer periphery of the optical lens to prevent the resin from flowing onto the surface of the optical lens during the injection molding of the frame. The frame is tightly bonded to the outer peripheral end face of the flat portion.
In a case where the lens frame is injection-molded around the outer periphery of the press-formed lens body, the problem arises that the bonding performance (tight bonding performance) of a joint surface or interface between the outer periphery of the lens body and the lens frame is insufficient. The insufficient bonding performance may result in separation of the lens frame from the lens body due to difference in expansion, which is caused by a change in environment temperature, or a curve or twist at the time of attaching the optical element device to a lens barrel.